Preparation of suspensions of water soluble solids in oleaginous media



United States Patent 3,065,174 Patented Nov. 20, 1962 3,065,174 PREPARATHBN F SUSPENSIGNS OF WATER SGLUBLE SOLEDS IN OLEAGHQOUS NEDIA Edward John Isiake and Walter Morrison, Sunbury-ou- Thames, England, assignors to The British Petroleum Company Limited, London, England, a joint-stock corporation of Great Britain No Drawing. Filed Get. 26, 1959, Ser. No. 848,537 Claims priority, application Great Britain Oct. 31, 1958 16 Claims. (Cl. 252-18) This invention relates to the preparation of suspensions of water-soluble solids in oleaginous media, such as hydrocarbons, in which the solids are insoluble.

It is often desired to incorporate water-soluble, oilinsoluble solids in oleaginous media, such as mineral lubricating oils and greases. For example, sodium nitrite at about 2% weight concentration is now frequently used as a corrosion inhibitor in lubricating grease. To be effective as a corrosion inhibitor and to eliminate any abrasive tendencies, the crystals of the sodium nitrite 20 must be stably dispersed and of very small particle size, preferably less than 5 microns. The same considerations also often apply to dispersions of other water-soluble solids in other oleaginous media.

One method of obtaining a stable suspension of finely divided particles is to use large amounts of petroleum sulphonates as dispersing agents but it has been stated that the compositions produced are very sensitive to the presence of water and, in the case of greases, tend to lose their structure.

Another method which has recently been proposed for this purpose is to emulsi-fy an aqueous solution of the solid with an oleaginous liquid to form a Water-in-oil emulsion using an emulsifying agent capable of forming such an emulsion, and thereafter heating the emulsion to drive off the water. However, when using the emulsitying agents suggested for this technique, e.g sodium stearate, sodium hydroxystearate, basic calcium alkylsulphonates and sodium alkyl sulphonate, poor dispersions with large individual crystal sizes were obtained.

We have now found that improved suspensions can be obtained by using a particular material as an emulsifying and dispersing agent.

According to the invention, there is provided a method of preparing a suspension of particles of a water-soluble solid in an oleaginous medium, in which an aqueous solution of the solid is emulsified with an oleaginous liquid to form a water-in-oil emulsion using beeswax as an emulsifying agent, and the emulsion is thereafter dehydrated.

The beeswax should preferably be one, the saponification value of which (as measured by IP 136/58) is at least 10, preferably at least 30, units greater than the acid value (as measured by IP 139/57).

In carrying out the method of the invention, the beeswax may conveniently be dissolved in the oleaginous liquid and the aqueous solution thereafter added. The emulsion may be produced by agitation of the mixture, e.g. by stirring, milling or both. Dehydration of the emulsion may be most conveniently effected by heating, e.g. at a temperature of 115 l70 C. During dehydration by heating it is advisable to continue stirring the emulsion to reduce foaming and to ensure that the emulsion does not break.

The oleaginous liquid may be a mineral oil, e.g. a lubrieating oil, a residue, a fuel oil or kerosine. It may also be a vegetable oil, e.g. castor oil, or a synthetic oil, e.g.

a diester, a polyglycol, a polyether or a silicon-containing synthetic oil. In order to produce a lubricating grease containing a dispersion of a water-soluble solid, a dispersion of the solid in lubricating oil prepared as described above may be either mixed with a grease or thickened to a grease consistency in known manner with a greaseforming agent.

Preferably the concentration of water-soluble solid in the final composition is 05-25% by Weight.

Preferably the amount of beeswax used is 01-10%, especially 0.5-7.5%, by weight on the oleaginous liquid.

In general it is desirable to use a fairly concentrated solution of the water-soluble solid as this reduces the amount of water which has to be removed from the emulsion. Solutions having a solids concentration of 20-70% wt. are particularly satisfactory.

Water soluble solids which can be suspended in oleaginous media by the method according to the invention include water-soluble corrosion inhibitors such as alkali metal and ammonium nitrites, carbonates, bicarbonates, sulphites, borates, chlorates, perchlorates, hypochlorites, silicates, phosphates, salicylates, citrates, tannates, lactates, tartrates, oxalates, phthalates, acetates, iodates, arsenites, chromates, molybdates and tungstates, and amine nitrites, phosphates and iodates. However, the invention is not limited to the use of water-soluble solids that are corrosion inhibitors. Examples of other water-soluble solids that may be used include watersoluble extreme pressure agents such as hydroxy fatty acids, polycarboxylic acids, hydroxy polycarboxylic acids, organic salts -(e.g. sodium benzoate), amides and amino acids.

A number of examples of the invention will now be described. The beeswax used in the examples had the following properties.

Colour Golden yellow.

Normal texture at room temperature Tough and flexible.

Melting point (1]? 133) 64 C.

Congealing point (IP 76) 62.2 C.

Acid value (1P 139/57) 14 mg. KOH/ g.

Saponification value (IP 136/58) 98 mg. KOH/ g.

Example 1 Two and a half grams of beeswax were dissolved in 100 grams of 150/75 grade lubricating oil (Redwood I viscosity at F.2150 seconds; viscosity indexz75) by warming and gently stirring. Fifteen grams of sodium nitrite crystals were dissolved in 30 grams of distilled water and this solution was emulsified with the oil/wax solution using a laboratory mixer operating at 3000 revolutions per minute. The water-in-oil emulsion so formed was then heated to 140 C. to drive off the water While high speed stirring was continued. (Heating to 140 C. took approximately 15 minutes and the dispersion was held at slightly over 140 C. for l-2 minutes.) The mix was then allowed to cool to atmospheric tem perature with gentle stirring.

On examining the anhydrous dispersion of sodium nitrite crystals in oil so formed, under the microscope using polarised light, it was found that a fine even dispersion of sodium nitrite crystals had been obtained, no individual crystal size being greater than 5 microns.

The above example was repeated using, in turn, potassium chromate, sodium benzoate and sodium tungstate in place of sodium nitrite. Again, fine even dispersions were obtained, no crystal size being greater than 5 microns.

Example 2 100 grams of beeswax were dissolved in 2000 grams of /75 grade lubricating oil by warming and stirring. 300 grams of sodium nitrite were dissolved in 400 grams of water and the oil and aqueous solution emulsified by slow speed stirring using a laboratory stirrer at approxi- 3 mately 100 revolutions per minute, followed by a milling step as described in Example 3.

The emulsion was then placed in a one gallon grease kettle provided with conventional slow speed stirring (i.e. approximately 25 revolutions per minute) as used for grease production, and heated to 140 C. whilst stirring. The heating time to 140 C. was about one hour and the material was held at about 140 C. for 1-2 minutes. The anhydrous suspension of sodium nitrite so obtained was very fine and well dispersed. No individual crystal size was greater than microns.

Example 3 grams of beeswax were dissolved in 500 grams of 150/75 grade lubricating oil. 75 grams of sodium nitrite were dissolved in 150 grams of distilled water and the oil and aqueous solution emulsified by high speed stirring using a laboratory stirrer, followed by milling between Carborundum stones set at 0.001 inch clearance and rotating at 3000 revolutions per minute. The emulsion was then dehydrated by heating to 140 C. with high speed stirring. (Heating time to 140 C. was approximately 30 minutes. The material was held at 140 C. for 1-2 minutes.) A =fine dispersion of sodium nitrite was obtained in which individual size was less than five microns.

A batch of lithium base grease was then made in known manner from:

405 grams hardened (hydrogenated) castor oil, 57 grams lithium hydroxide monohydrate, and 2038 grams mineral lubricating oil (150/75 grade).

Penetration at C.worked:

60 strokes (1P 50/56) 244 mm./l0. Penetration at 25 C.worked: 100,000 strokes (IP 50/56) 278 mm./10. Drop point (IP 31) 182 C. Oil separation on storage at 25 C. (IP 121/57) 0.1% wt. Bleed test (DTD 825A) 1.5% wt.

Penetration at 25 C. after 4 hours in Shell Roll tester at room temperature (SMS 466)--- 239 mm./ 10. Penetration at 25 C. after 4 hours in Shell Roll tester at 100 C. (SMS 466) 283 mm./10. NaNO particle size Less than 5 Corrosion test No resting observed.

No difficulties were experienced in pumping the grease through a 200 mesh BSS sieve and no agglomeration or crystal growth was observed in the grease after two months storage.

Example 4 By way of comparison, a lithium base grease was made in the same manner as in Example 2 using the following ingredients:

Mineral lubricating oil a (150/75 grade) vHardened castor oil 13.0% wt. Lithium hydroxide monohydrate 1 1.8% wt.

No sodium nitrite was added. Inspection data were as follows:

(SMS 466) 336 mrn./10. Drop point (IP 31) 189 C. Oil separation on storage at 25 C. (IP 121/57) 2.4% wt. Bleed test (DTD 825A) 3.9% wt. Corrosion test Severe rusting on all bearing parts.

It appears from the above data that the presence of sodium nitrite in a lithium grease may cause a slight lowering of drop point but this is not significant in terms of rig performance and the drop point of the grease of Example 3 is as good as the drop points of currently marketed lithium greases containing sodium nitrite.

The mill used in the above examples was a Premier colloid paste mill. This is a high speed mill (3000 revolutions per minute) in which the material to be milled is fed between a 5 inch Carborundum rotor and a Carborundum stator, the annular gap being variable up to 0.025 inch.

The corrosion test was carried out in a ring consisting essentially of a 35 millimetre bore, double row, selfaligning ball race fitted with a pressed steel cage and housed in a plummer block. It was operated at revolutions per minute and with no load applied.

The bearing is filled with the grease under test and the housing is packed in such a way as to form a cup round the bearing, 20 millilitres of water are introduced into this cup.

The rig is run (with Water present) on 3 consecutive days for 8 hours each day followed by a 3-4 day static period. At the end of this static period the bearing parts are examined for rusting and corrosion.

The use of beeswax in producing the dispersions according to the invention has the following advantages:

(a) It is readily available and relatively cheap. No elaborate processing or extraction procedures are required for its production. The production of a grease containing a stable dispersion of sodium nitrite as described above does not result in any darkening of the colour of the grease. It is not necessary to use evaporation on heated drums or recirculation through fine nozzles during the dehydration step as mentioned in previous proposals for producing dispersions by the emulsification technique. I As shown by Example 2, facilities for high speed stirring are not required to produce the dispersions. Satisfactory corrosion-inhibited greases may be made using conventional and established grease making equipment, i.e. mills used for grease production and normal open grease kettles.

We claim:

1. A method of preparing a suspension of particles of a water-soluble solid in an oleaginous medium which comprises emulsifying an aqueous solution of the solid with an oleaginous liquid and beeswax to form a waterin-oil emulsion, and thereafter dehydrating the emulsion.

2. A method according to claim 1, in which the beeswax has a saponification value of at least 10 units greater than its acid value.

3. A method according to claim 2, in which the beeswax has a saponification value of at least 30 units greater than its acid value.

4. A method according to claim 1, in which the beeswax is dissolved in the oleaginous liquid and the aqueous solution thereafter added.

5. A method according to claim 1, in which the emulsion is produced by agitating the oleaginous and aqueous phases.

6. A method according to claim 1, in which the dehydration of the emulsion is effected by heating.

7. A method according to claim 6, in which the heating is carried out at a temperature of 115170 C.

8. A method according to claim 1, in which the oleaginouS liquid is a lubricating oil.

9. A method according to claim 8, in which the lubricating oil is a mineral lubricating oil.

10. A method according to claim 1, in which the amount of beeswax used is 0.1-% by weight of the oleaginous liquid.

11. A method according to claim 10, in which the amount of beeswax used is 05-75% by weight of the oleaginous liquid.

12. A method according to claim 1, in which the aqueous solution has a solids concentration of 20-70% by weight.

13. A method according to claim 1, in which the concentration of water-soluble solid suspended in the final composition is 05-25 by weight.

14. A method according to claim 1, in which the watersoluble solid is sodium nitrite.

15. In a method of preparing a lubricating grease containing a suspension of particles of a water-soluble solid, the improvement which comprises emulsifying an aqueous solution of the solid with a lubricating oil and beeswax to form a water-in-oil emulsion, dehydrating the emulsion so formed and mixing the resulting suspension with a grease.

16. In a method of preparing a lubricating grease containing a suspension of particles of a water-soluble solid, the improvement which comprises emulsifying an aqueous solution of the solid with a lubricating oil and beeswax to form a water-in-oil emulsion, dehydrating the emulsion so formed and thickening the resulting suspension to a grease consistency with a grease-forming agent.

References Cited in the file of this patent UNITED STATES PATENTS 2,235,161 Morway et al. Mar. 18, 1941 2,342,199 Hurtt Feb. 22, 1944 2,758,085 Oberright Aug. 7, 1956 FOREIGN PATENTS 778,822 Great Britain July 10, 1957 UNITED STATES PATENT OFFICE CERTIFICATE, OF QORRECTIGN Patent N0 3,065,174 November 20 1962 Edward John Blake et al8 ppears in the above numbered pat- It is hereby certified that error a id Letters Patent should read as ent requiring correction and that the sa corrected below.

line 59 for "resting" read rusting Column 3,

for "251 mma/lO." read 289 mmo/lO.

column 4, line 6,

Signed and sealed this 11th day of June 19639 (SEAL) Anna:

DAVH)L.LADD

ERNEST W. SWIDER Attesting Officer Commissioner of Patents UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent N00 3,065, 174 November 20 1962 Edward John Blake et ale It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below Column 3 line 59, for "resting" read rusting column 4, line 6 for "251 mmQ/IO," read 289 mmD/IO.

Signed and sealedthis 11th day of June 1963.,

(SEAL) Attest: ERNEST w. 'SWIDER DAVID LADD Commissioner of Patents Attesting Officer 

15. IN A METHOD OF PREPARING A LUBRICATING GREASE CONTAINING A SUSPENSION OF PARTICLES OF A WATER-SOLUBLE SOLID, THE IMPROVEMENT WHICH COMPRISES EMULSIFYING AN AQUEOUS SOLUTION OF THE SOLID WITH A LUBRICATING OIL AND BEESWAX TO FORM A WATER-IN-OIL EMULSION, DEHYDRATING THE EMULSION SO FORMED AND MIXING THE RESULTING SUSPENSION WITH A GREASE. 